As a technique of this type of printing apparatus, there are known the techniques disclosed in, for example, Unexamined Japanese Patent Publication No. 54-152504 (corresponding to U.S. Pat. No. 4,280,406), Examined Japanese Patent Publication No. 55-28860 (corresponding to U.S. Pat. No. 4,141,293), and Examined Japanese Patent Publication No. 3-71983. All of the above mentioned publications are incorporated by reference.
In the printing apparatus of Unexamined Japanese Patent Publication No. 54-152504, as shown in FIG. 29, plate cylinders 1041 to 1044 and blanket cylinders 1051 to 1054, which were positioned at an ink coating apparatus setting side separately from a feeding side for web paper and a discharging side for paper cut into sheets, were arranged in the same frame to be slidably drawn. This resulted in easy plate replacements, and easy change of a print format, and operability of the printing apparatus was improved.
In Examined Japanese Patent Publication No. 55-28860, as shown in FIG. 30, in order to carry out multicolor printing on continuous paper, a plurality of print units was vertically arranged, thereby reducing a setting floor area for the printing apparatus. Also, the ink coating apparatus were provided on the same side, so that easy plate replacements were achieved. In the printing apparatus of Examined Japanese Patent Publication No.3-71983, as shown in FIG. 31, spaces for setting dampening water apparatuses are omitted by use of waterless plates. Instead, a plate feed and discharge device was provided to the omitted space for each plate cylinder so as to improve operability.
As a technique of the coating apparatus used in these printing apparatus, there are known the techniques disclosed in, for example, Unexamined Japanese Patent Publication No. 57-178872, Unexamined Japanese Utility Model Publication No. 56-76438, and Examined Japanese Patent Publication No.4-68147. These techniques are used as an ink coating technique for the printing apparatus, and frequently employed mainly in waterless lithographic printing, a letterpress printing, etc. In particular, Examined Japanese Patent Publication No. 4-68147 disclosed a coating apparatus having a coating roller with an elastic surface, and a doctor blade, which freely moved back and forth to the outer peripheral surface of the coating roller and controlled a thickness of a coated ink film to be formed on the outer peripheral surface. This was an extremely useful coating technique when ink having high viscosity was used.
The feature of the techniques used in these coating apparatus is that the doctor blade is used as a method for setting the thickness of the ink film to be applied onto the coating roller. For example, in the technique of Examined Japanese Patent Publication No. 4-68147, as shown in FIG. 32, an ink unit 1002, serving as an ink coating apparatus, comprises a form roller 1201, a doctor blade 1202, an eccentric cam 1203 for controlling the movement of the doctor blade, ink distributing rollers 1210, 1211, and an auxiliary form roller 1212 having an elastic surface. The form roller 1201, the doctor blade 1202, side plates 1207 and 1208, which are arranged at both sides of the form roller 1201 in its axial direction, and an ink fountain 1206 form an ink fountain space 1205, which is filled with printing ink i.
A small gear (not shown) rotating solidly with the form roller 1201 is engaged with a large gear (not shown) rotating solidly with a plate cylinder 1015. Thus, the form roller 1201 and the plate cylinder 1015 are synchronized with each other and rotated at the same circumferential speed at their contact section.
The ink unit 1002 is configured so that the eccentric cam 1203 attached to a shaft 1204 is rotated so as to move the doctor blade 1202 back and fourth in a direction of an arrow A, thereby changing the engagement between the doctor blade 1202 and the form roller 1201 in order to control the thickness of the coated ink film formed on the outer periphery of the form roller 1201.
Conventionally, a printing plate, serving as an imaging medium used in such a printing apparatus, has been generally manufactured by a photomechanical process in which a lith type film (lithographic film) for plate-making is applied to a PS plate (presensitized plate or the like). Since the plate-making apparatus and the printing apparatus are normally independent devices, the positioning of the imaging medium of each color in the multicolor printing is carried out by the following process.
At the outset register marks were drawn on the imaging medium for each color. Then, the imaging medium for each color was installed around each plate cylinder of the printing apparatus. Ink was fed to the imaging medium of each color, and printing was performed on a recording medium such as paper. Then, the positions of the imaging mediums of the respective colors in the printing apparatus and the print timing were adjusted until the positions of the register marks printed on the recording mediums of the respective colors coincided with each other. Thus the mutual positions of the imaging mediums of the respective colors were determined.
In recent years, there has been increased the use of the imaging apparatus for making the printing plate, which serves as the imaging medium, based on digital imaging information in accordance with imaging data. As an imaging medium fixing method in these imaging apparatuses, there are known techniques disclosed in Unexamined Japanese Patent Publication No.3-24549 (corresponding to U.S. Pat. No.5,094,933) and Unexamined Japanese Patent Publication No. 5-8366, which are incorporated by reference.
In the apparatus of Unexamined Japanese Patent Publication No. 3-24549, as shown in FIG. 33, after imaging on a web imaging medium, the imaging medium is cut to a predetermined size, developed and carried by a transfer roller or a conveyor belt.
In Unexamined Japanese Patent Publication No. 5-8366, as shown in FIG. 34, the imaging medium is wound around an attaching member and rotated, and imaging is executed by irradiation of an energy beam. The imaging medium is fixed to the plate cylinders with flat-headed screws, or adhered thereto with adhesive.
As a technique in which the imaging medium is wound around an attaching member and rotated, and imaging is executed by irradiation of the energy beam, the imaging apparatus disclosed in Unexamined Japanese Patent Publication No. 5-8366 was configured as described as follows.
That is, the attaching member to which the imaging medium was attached was rotated and the energy beam scans in a circumferential direction of the imaging medium. Also, the laser block having a semiconductor laser is scanned in the axial direction of the attaching member by use of a ball screw.
The shaft of the attaching member and the ball screw are arranged to be parallel with the axial direction of the attaching member. The scanning in the axial direction is executed for each scanning in the circumferential direction while the attaching member is rotated. The scanning is performed over the entire surface of the imaging medium thereby imaging is executed.
The imaging apparatus disclosed in Unexamined Japanese Patent Publication No. 8-72311 is configured as follows.
That is, as shown in FIG. 35, the imaging medium, which is wound around the attaching member and rotates, is irradiated with the energy beam from a plurality of recording heads having a plurality of energy beam irradiation sources, so as to execute imaging. The imaging medium, which is wound around the attaching member and rotates, is scanned in the circumferential direction by its rotation and simultaneously, the recording heads are scanned in the axial direction of the attaching member by a linear motor, etc. Therefore, the rotation shaft of the attaching member and a carriage apparatus such as a linear motor, which scans the plurality of recording heads in the axial direction of the attaching member, are arranged in parallel with respect to the axial direction of the attaching member.
The energy beam irradiation position is determined by detecting means for detecting the position of a beam spot light of the energy beam and means for correcting the irradiation position of the beam spot light to the attaching member based on the output from the detecting means.
In the printing apparatus of Unexamined Japanese Patent Publication No. 54-152504 shown in FIG. 29, there was a problem in that it was impossible to carry out a back face printing after feeding a sheet of paper. When the interval between grippers for gripping paper on an impression cylinder 1031 in the circumferential direction is shorter than a length of the sheet of paper to be printed in the progress direction the paper is sandwiched between the pressure cylinder 1031 and blanket cylinders at two portions simultaneously so that the paper is suffered some tension. As a result, the printing position may shift, which is a problem. Moreover, if the interval between the grippers for gripping paper is increased in order to solve the problem, the ink coating apparatuses could not be arranged for three or more color printing, which is also a problem.
On the other hand, if the impression cylinder 1031 is enlarged in order to arrange the ink coating apparatus, the diameter of the impression cylinder 1031 becomes too large, and the entire printing apparatus must be enlarged. As a result, a large setting space for such a printing apparatus was required and the cost of the impression cylinder 1031 was increased, so that the printing apparatus became expensive.
The method disclosed in Examined Japanese Patent Publication No. 55-28860 was limited to the printing apparatus using continuous webs, and could not be applied to the printing apparatus using sheets of paper. In the technique disclosed in Examined Japanese Patent Publication No. 3-71983, since one blanket cylinder was shared by two ink coating apparatus, there occurred a problem in which process color printing could not be carried out. Also, since one blanket cylinder was shared by two ink coating apparatus, the distance of the ink coating apparatus could not be increased due to the structure of the printing apparatus, so that workability of plate replacements became worse. In the technique disclosed in Examined Japanese Patent Publication No. 3-71983, a plate feeding and discharging apparatus was used to improve workability. Though the plate was easily replaced by use of the plate feeding and discharging apparatus, there occurred a problem in which the printing apparatus became expensive.
In the ink coating apparatus disclosed in Examined Japanese Patent Publication No. 4-68147, there was a problem in which striped defects were generated in the circumferential direction of the surface of the coated ink film because of paper dust clogged at the doctor blade portion as shown in FIG. 6. In other words, when the doctor blade portion is clogged with paper dust, a form roller 1201 bends at the clogging portion and escapes therefrom. Since the thickness of the ink layer of this portion is increased and the portion between the doctor blade 1202 and the form roller 1201 is clogged with paper dust, striped defects 1252 are generated in an ink layer in the circumferential direction.
Since the defects were left in the ink layer on the coating roller as a deep groove, such troublesome defects could not be easily eliminated even if the distributing roller is simply used.
In the imaging apparatus disclosed in Unexamined Japanese Patent Publication No. 3-24549, the printing plate, which is the imaging medium exposed and developed, is cut by a built-in cutting apparatus, thereafter the printing plate is automatically on the imaging apparatus. According to such the imaging apparatus, the positioning of the mutual printing positions of imaging mediums of the respective colors was not accurately made in the multicolor printing apparatus. As a result, there was a problem in which the mutual printing positions of imaging mediums of the respective colors had to be adjusted again before continuous printing was executed.
Unexamined Japanese Patent Publication No. 5-8366 describes a method in which the imaging medium is fixed to the plate cylinder with a flat-headed screw, or adhered thereto with adhesive. However, the positioning of the imaging medium and that of the print pattern cannot be accurately made. Moreover, this publication describes no specific method other than the positioning of the imaging medium and that of the print pattern. Therefore, in the imaging medium prepared by the apparatus as described in Unexamined Japanese Patent Publication No. 5-8366, there was no other way than the aforementioned method of positioning the register marks in connection with the positioning method at attaching of the imaging medium to the printing apparatus.
On the other hand, the printing apparatus having a laser head for imaging is known. In this apparatus, imaging is executed after imaging medium is wound around the plate cylinder, and ink is directly fed and printing is executed. In this apparatus, if the positional relationship between the plate cylinder and the imaging head are made to completely corresponding to each other for each color, the positioning of the imaging medium can be omitted or largely simplified at the printing time.
However, the above printing apparatus can neither perform imaging during the printing and nor print during the imaging when the imaging head is provided therein. It cannot avoid a decrease in productivity as a printing apparatus or independent apparatus. In addition, since the imaging head occupies most of the manufacturing cost of the imaging apparatus. If the head is provided for each plate cylinder of each color, the manufacturing cost of the entire apparatus is largely increased. One imaging apparatus is not necessary for one printing apparatus. Generally, imaging mediums to be used for many printing apparatus are made by one imaging apparatus. As compared with the case in which the printing apparatus and the imaging apparatus are separately provided as a different structure the structure in which the imaging apparatus is provided in the printing apparatus as in the above-mentioned apparatus has demerits in terms of productivity and the manufacturing cost.
As explained above, the mutual positioning of the image patterns for the respective colors in the multicolor printing was performed as the follows. That is, the positioning was made by adjusting the position of the plates in the printing apparatus and the timing such that the positions of the register marks printed on the recording mediums for the respective colors were coincide with each other.
Hence, simple installing of the imaging medium S which were directly prepared by the imaging apparatus to the printing apparatus cannot achieve accurate positioning of the imaging mediums.
Moreover, there has been no imaging apparatus in which some contrivance was added to a positioning hole size, which was necessary for adjusting the positions of the imaging mediums, and chamfering of end portions of the imaging mediums for another reason. Moreover, there was no imaging apparatus in which the imaging medium attaching member was subjected to a surface coating process to improve accuracy of attaching the imaging medium to the imaging apparatus.
In the configuration that a beam irradiation apparatus having a plurality of beam irradiation sources is continuously scanned in the direction of a rotation axis of the attaching member at a fixed speed as continuously rotating the attaching member around which the imaging medium is wound at a fixed speed, there was a problem in which the image was obliquely formed with respect to a reference direction of an original imaging area of the imaging medium.
In the imaging apparatus as shown in FIG. 34, the imaging medium is rotated in a direction of an arrow R (rotational direction of the attaching member) at peripheral speed Vr, and that the beam irradiation apparatus is scanned in a direction of an arrow S (direction of a rotation axis of the attaching member) at feeding speed Vy. As shown in FIG. 27A, it would be ideal if imaging dots 2092 formed in an imaging area 2091 of an imaging medium 2018 would be arranged in a matrix form of rectangle along an arrow direction 93 of the imaging area 2091.
However, in the imaging apparatus as shown in FIG. 34, since the beam irradiation apparatus is scanned in the direction of the rotation axis of the attaching member as rotating the attaching member, if the imaging medium 2018 is fixed to a plate cylinder 2011, serving as the attaching member, such that the reference direction of the imaging area is parallel to the rotation axis of the plate cylinder 2011, and the scanning direction of the beam irradiation apparatus completely coincide with the direction of an arrow S (.theta.=0 in FIGS. 27A to 27C), there occurred a problem in which the imaging dots 2092 were deformed to be a parallelogram as shown in FIGS. 27B and 27C.
A first object of the present invention is to provide a multicolor printing apparatus in which the disadvantages of the prior art can be improved in that a back face printing can be easily carried out, and a good workability can be obtained.
A second object of the present invention is to provide a multicolor printing apparatus in which a good printing quality can be obtained, no large space is necessary for setting a printing apparatus, and a manufacturing cost is reasonable.
A third object of the present invention is to provide an duplex printing method for providing a good printing quality at a small space easily.
A fourth object of the present invention is to provide a coating apparatus in which disadvantages of the prior art can be improved and striped defects are not easily generated in the circumferential direction of the surface of the coated ink film because of paper dust even when ink having high viscosity is coated.
A fifth object of the present invention is to provide an imaging apparatus in which the disadvantages of the prior art can be improved in that the positioning of the printing position at printing in that can be easily realized in a state that an imaging apparatus and a printing apparatus are maintained as independent structures, and provide a printing apparatus and printing system, and an imaging method, and a printing method.
A sixth object of the present invention is to provide an imaging apparatus with a reasonable cost in which disadvantages of the prior art can be improved in that an image can be formed without having an inclination with respect to the imaging medium, the positioning of the imaging medium at an imaging time can be easily carried out where an imaging apparatus and a printing apparatus are independent structures, and an inclination of the image position in the imaging medium can be restrained and corrected, so that the positioning of printing plate in a printing apparatus can be easily carried out, and provide an imaging method and a printing system.